Analog-to-digital converters, or ADCs, convert real world signals such as audio and video to digital signals where they can be processed by digital processors. Common examples include the cell phone where the analog voice of the user is converted for digital processing and transmission. Another example is the video recorder that takes in analog signals representing a picture or scene. The analog-to-digital converter changes these analog signals to digital form for processing and storage.
At a high level, an ADC may be represented by a component with an analog input and a digital output. The analog input represents signals such as voice or video, although countless other representations are possible. The output also represents the input signal but in a digital form of ones and zeros. The speed at which the input changes in time and the accuracy or fidelity of the digital output signal determine the type of ADC needed.
Speed, power consumption, cost and noise are all considerations in the design of analog-to-digital converters. Many types of analog-to-digital converters are in use, each with its owns strengths and weaknesses.
Currently the classic pipelined or Flash analog-to-digital converter (ADC) must operate the ADC clock at the desired sample frequency. Higher sample rates can sometimes be achieved with double clock sampling where parallel ADC stages are clocked on opposite edges of the ADC clock. Other approaches parallel several ADCs. One example of parallel ADCs has eight identical ADCs operating in parallel. While each ADC is clocked at the conversion clock frequency f, the overall conversion rate is eight times f, (8*f). However, even though the bandwidth of the parallel conversion system increases by a factor of 8, the signal-to-noise ratio (SNR) is unaffected at best. In other, non-parallel cases, higher sample rates require higher clock speeds. Higher clock speeds place more constraints on the semiconductor processes, matching of components and post fabrication trimming and calibration.